Technical Field
Embodiments of the invention relate generally to vehicle control. Certain embodiments relate to systems and methods for reducing fuel consumption in a vehicle in a dynamic braking mode of operation.
Discussion of Art
In the mining industry, large off-highway vehicles, “OHVs”, usually employ electrically motorized wheels for propelling or retarding the vehicle. In particular, OHVs typically include a large horsepower diesel engine in conjunction with an alternator, a traction inverter, and wheel drive assemblies housed within the rear tires of the vehicle. In operation, the diesel engine drives the alternator, which powers the traction inverter. The traction inverter includes semiconductor power switches that commutate the alternator output current to provide electrical power to electric drive motors, e.g., AC traction motors, of the wheel drive assemblies, which transform the electrical power back into mechanical power to drive the wheels and propel the vehicle.
As is understood in the art, the traction motors provide the tractive power to propel the vehicle. The traction motors are also configured to provide a braking force for controlling speed or for slowing the vehicle. This is commonly referred to as dynamic braking. Simply stated, when a traction motor is not needed to provide motive force, it can be reconfigured so that the motor operates as a power generator. So configured, the traction motor generates electric energy which has the effect of slowing the vehicle. In certain vehicles and systems, the electrical energy is stored in batteries for later use or, more commonly, dissipated via retarding grids. In particular, some vehicles and systems are configured to store the electrical energy provided by the motor during dynamic braking in energy storage devices or batteries for later use. This stored energy is used to power auxiliary devices and/or drive motors during idling or propel modes of operation so as to minimize engine involvement and reduce fuel consumption.
A favored alternative to storage configurations serves to simply waste the energy in the form of heat via a dynamic braking retarding grid of resistors and insulators. A drawback to this, however, is that a grid cooling system having an electrically driven blower is often necessary to help dissipate heat from the grid, which adds to power demand and thus increases fuel consumption.
Even during dynamic braking, the engine continues to consume fuel to meet the electrical needs and auxiliary loads of the vehicle. For example, this includes providing power for traction motor blowers, radiator fans, operator cab heater or air conditioner alternator blower, hydraulic pumps, etc. In the case of OHVs, this includes providing power for cooling fans to cool all components in the traction drive system.
In view of the above, there is a need for a system and method which reduces fuel consumption during dynamic braking modes of operation by reclaiming dynamic braking energy, and which improves the overall efficiency of an electric drive machine.